Radio frequency patient heating system

ABSTRACT

The system of the present invention includes a heat exchange catheter for warming flowing blood within a blood vessel. The heat exchange catheter includes a catheter body having a proximal end and a distal end with electrodes. The electrodes generate an electric field that radiates heat to the flowing blood. The electrodes comprise discrete bands that serially align and are spaced apart from each other. Each electrode has a polarity, and for each electrode there is an adjacent electrode having an opposite polarity. A support centrally aligns the catheter body within the blood vessel.

PRIORITY

[0001] Priority of application Ser. No. 60/256,090 filed on Dec. 15,2000 in the United States of America with the USPTO is claimed under 35U.S.C. §119(e).

FIELD

[0002] This invention relates to devices and methods for transferringthermal energy to a patient, and more particularly vascular cathetersand systems for dispelling hypothermia.

BACKGROUND

[0003] It is common for patients surgical procedures, to experience mildto severe hypothermia. There are numerous causes for this decrease ofbody temperature. One cause pertains to anesthesia. Anesthesia maydepress the body's set-point temperature as regulated by the brain'sthermal control center.

[0004] Another cause for decreased body temperature during surgery maymanifest when the patient has his or her thoracic or abdominal cavityopened. This greatly increases the amount of surface area exposed to theatmosphere and thereby accelerates loss of body heat. As a rule,surgical suites are kept very cool. Cool surgical suites can makepatients cold.

[0005] Several surgical procedures (e.g., coronary bypass grafts, valvereplacements, etc.) utilize intentional hypothermia in order to decreasethe body's energy demands during the procedure. These patients need toreturn from a deep hypothermic state to a normal body temperaturefollowing the procedure.

[0006] Current methods of treating the hypothermic patient include hotbaths, delivering warm fluids orally and applying heating blankets.Heating blankets use either air or liquid as the heat-transfer medium.If placed below the patient, a heating blanket transfers thermal energyto the patient by a combination of conduction and convection. Conductiveheating results from intimate, pressured, contact with the skin of apatient. Convective heating results from using a local air film betweenthe blanket surface and a patient's skin to convectively heat thepatient.

[0007] Some air type heating blankets are placed over the patient, andsupply warm air under low pressure via the blanket. The warm air “leaks”out of the blanket at low velocity and with reasonable uniformity overits surface to warm the patient. Heating blankets transfer heat throughthe patient's skin surface, relying principally on the vascular systemto transfer the thermal energy to the patient's core via the blood flow.

[0008] The rate of heat transfer, and therefore the effectiveness, of aheat-blanket warming system is limited by the body's natural response tolow core temperatures. Such a response may include “shutting down” bloodflow to the extremities. The body may also sweat in response toapplication of a heating blanket. Sweating cools the body and reducesthe effectiveness of heating blankets.

[0009] The heating blanket approach is sometimes used in conjunctionwith other ways of heating the patient, such as heating the blood supplydirectly. U.S. Pat. No. 5,837,003 to Ginsburg, issued Nov. 17, 1998,discloses an exemplary way of using an electrically resistive heater atthe end of a catheter to heat the blood supply of a patient. Heating theblood supply, in conjunction with blankets and other ways of heating thepatient, can shorten the time required to bring a patient tonormothermia.

[0010] One drawback to the invention disclosed by Ginsburg is that inorder to transfer a significant amount of heat to the blood supply, theresistive element would have to be very hot. It is known, however, thatblood heated over 42 degrees C., or so, may coagulate. Accordingly, themaximum temperature at which the resistive elements operate isrestricted by the tendency of the blood to coagulate.

[0011] In an effort to provide a catheter that can transfer heat atrelatively lower temperatures, the catheter surface area has beenincreased. One design increases the distal diameter of the catheter (SeeU.S. Pat. No. 5,837,003 FIG. 7). Other designs show helical fins,annular fins and axial fins, respectively. (U.S. Pat. No. 5,837,003FIGS. 8a, 8b, and 8c). The fins maximize the surface area of thecatheter in contact with the blood supply and, thereby, improve theability of the catheter to conduct heat to the blood supply.

[0012] Maximizing the area of a heating surface on a catheter is notwholly effective. One reason for this is that increasing the diameter ofa catheter impedes blood flow, which, may reduce the effectiveness ofany heat transfer between the catheter and the blood supply. Further,fins may impede blood flow in regions adjacent the fins, causing theblood to overheat. Blood that overheats could coagulate on the fins.

[0013] Fins, by themselves, are somewhat inefficient. Much of the bloodthat passes the catheter does not contact the fins or heat exchangeelements and therefore, may not undergo a significant temperaturechange.

[0014] What is desired is a catheter that does not significantly impedeblood flow. What is also desired is a catheter with improved heattransfer capability without overheating the blood.

SUMMARY

[0015] The system of the present invention includes a heat exchangecatheter for warming flowing blood within a blood vessel, or for warmingtissue in any body cavity. The heat exchange catheter includes acatheter body having a proximal end and a distal end with electrodes andtemperature sensor elements.

[0016] The electrodes generate an electric field that radiates into theflowing blood. Heating of the blood results when the electric fieldexerts one of two possible effects on the blood, depending on thefrequency of the energy and whether the electrodes are in direct ohmiccontact with the blood.

[0017] It is understood that the electric field accelerates freeelectrons in the blood, creating a flow of localized electric currentsin the blood. The electric currents flowing through the blood causeresistive heating of the fluid through the relationship P=I²R, where Pis power, I is the RMS current and R is the blood resistance.

[0018] It is also understood that the electric field is absorbed,principally by the water molecules that make up the bulk of the bloodvolume. Dielectric loss in the water molecules converts the electricfield energy to thermal energy.

[0019] The electrodes comprise discrete bands that serially align andspace apart from each other. Each electrode has a polarity, and for eachelectrode there is an adjacent electrode having an opposite polarity.The electric field is generated between the electrodes of opposingpolarities, and the electric field extends radially out from the bandsto heat flowing blood.

[0020] While the electric field is used to heat the blood, it isenvisioned that additional forms of heating can be used in conjunctionwith the heating method of the present invention such as havingresistive heating elements in or on the catheter, and having acirculating heating fluid within the catheter.

[0021] The system includes a control unit coupled with the catheter viaelectric cabling for powering the electrodes with radio frequency (RF)energy. The control unit provides alternating current to the electrodesin the RF frequency range (i.e., between 100 kHz to 3,000 kHz).Preferably, the current is at about 500 kHz to generate an electricfield of a corresponding frequency.

[0022] To optimize the heating effects of the electrodes, the catheterincludes a selectively deployable support for positioning the electrodescentrally within the blood vessel. Ideally the support gently holds thecatheter within the blood vessel by gently pressing against the walls ofthe blood vessel. Central positioning of the catheter optimizes heatexchange between the catheter and the blood. The support, according toone aspect of the invention, is adjustable in length.

[0023] The support is described in terms of multiple possibleembodiments. A according to one embodiment the catheter has multiplesupports comprising flattened wires having ends and lengths. The ends ofthe supports attach to the catheter body. The lengths alignlongitudinally along the catheter body to selectively deploy against theblood vessel wall to center the catheter body within the blood vessel.Preferably, the distal end of the catheter body includes a switchmechanically coupled with the supports to selectively deploy thesupports. Alternately, automatically deployable supports are providedthat deploy in response to removal of an insertion tube, or similardevice.

[0024] Variations of this embodiment include an aspect having the endsof the supports attaching to the catheter body in a position proximalthe electrodes. Another aspect has the supports attaching to thecatheter body in a position distal the electrodes. Yet another aspecthas one end of each support attaching to the catheter body in a positionproximal the electrodes, and the other end of each support attaching tothe catheter body distal the electrodes.

[0025] According to another embodiment, the supports have pins thatradially extend from the catheter body to bear gently against the bloodvessel.

[0026] According to another embodiment, each support includes a ring andextensions. The extensions support the ring to selectively deploy thering from a first configuration where the ring lies flush along thecatheter body to a second configuration where the ring gently pressesagainst the blood vessel. The extensions and ring cooperate to permitblood to flow past the extensions when the ring holds the catheter bodycentrally within the blood vessel. According to one aspect of thisembodiment, the extensions extend at an oblique angle from the catheterbody to the ring so that the extensions and the ring form a frustumshape.

[0027] One aspect of this embodiment manifests where the ring andextensions form a web. The web circumscribes the catheter body, the webbeing selectively deployable from a first configuration where the weblies on the catheter body, to a second configuration where the webextends from the catheter body to the blood vessel. The web permitsblood to flow through the web when the web holds the catheter bodycentrally within the blood vessel. The web achieves a frustum shape inthe second configuration, according to a variation of the invention.According to a further variation, the web comprises a resistive heatingelements which conducts RF current and cooperate with the electrodes towarm the blood.

[0028] According to yet another embodiment, the blood vessel has a walland the support includes a helical wire for contacting the wall of theblood vessel along a helical path. The helical wire is distanced fromthe distal end of the catheter body to facilitate blood flow between thehelical wire and the catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention is described in terms of various embodiments,reflected in the figures, wherein like parts have like referencenumerals, and wherein:

[0030]FIG. 1 is a perspective view of a system in accordance with thepresent invention.

[0031]FIG. 2(a) is a perspective view of the distal end of a catheterbody in accordance with the present invention.

[0032]FIG. 2(b) is a cross-sectional view of the catheter body of FIG.2(a) as seen along the line 2(b)-2(b).

[0033]FIG. 3 is a perspective view of an embodiment of the distal end ofa catheter body in accordance with the present invention.

[0034]FIG. 4 is a perspective view of an embodiment of the distal end ofa catheter body in accordance with the present invention.

[0035]FIG. 5 is a perspective view of an embodiment of the distal end ofa catheter body in accordance with the present invention.

[0036]FIG. 6 is a perspective view of an embodiment of the distal end ofa catheter body in accordance with the present invention.

[0037]FIG. 7 is a perspective view of an embodiment of the distal end ofa catheter body in accordance with the present invention.

[0038]FIG. 8 is a perspective view of an embodiment of the distal end ofa catheter body in accordance with the present invention.

DETAILED DESCRIPTION

[0039]FIG. 1 shows a radio frequency patient heating system generallydesignated with the reference numeral 10. The heating system 10 includesa control unit 12 and a catheter generally designated with the referencenumeral 13. The catheter 13 has a catheter body 14. The catheter body 14has a proximal end 16, a distal end 18, deployable supports 22, a tip24, an infusion lumen 26 with an ejection port 28, and a switch 30. Thesystem 10 includes an electrical cable 32 connecting the control unit 12and the catheter body 14.

[0040] The catheter body 14 includes a long (60 to 120 cm), thin (1 to 4mm diameter, 3 to 12 French) cylindrical tube of a biocompatible polymerwith stiffness balanced for flexibility and “push-ability”.

[0041] The electrodes 20 mount on the distal end 18 of the catheter body14. According to one aspect of the invention, the electrodes 20 comprisediscrete bands that circumscribe the catheter body. The electrodes 20are formed from a radiopaque alloy. Preferably, the electrodes are madefrom a platinum-iridium alloy or a stainless steel material. Fineconductors thread through the catheter body 14 to electronically couplethe electrodes 20 via the distal end 16 of the catheter body 14 to thecontrol unit 12.

[0042] During operation, and at any given moment, each electrode 20 hasa polarity. For each electrode 20 there is an adjacent electrode havingan opposite polarity. This creates an electric field between adjacentelectrodes 20. The electric field is adapted to heat blood.

[0043] The infusion lunien 26 facilitates infusion of fluid such asmedicine, nutrition, or contrast agent. Contrast agent infusion enablesverification of (dye) in alignment and placement of the distal end 18 ofthe catheter body 14 within a blood vessel. The contrast agent injectsvia the infusion lumen 26 directly into flowing blood. The contrastagent exits the catheter body 14 via the ejection port 28, which islocated on the distal end 18 of the catheter body 14 in a positionproximal to the electrodes 20. It can be appreciated that fluidsincluding medicinal fluids, blood thinners, etc. can be infused directlyinto the flowing blood via the infusion lumen 26.

[0044] The proximal end 16 of the catheter body 14 includes a handle 36.The handle 36 is used for holding and manipulating the catheter 13during introduction, alignment and withdrawal of the catheter 13 fromthe patient. The handle 36 regulates contrast agent infusion accordingto one aspect of the invention.

[0045] The handle 36 houses the switch 30. The switch 30 mechanicallycouples with the supports 22. The switch 30 reciprocates to selectivelydeploy and retract the supports 22. According to an alternateembodiment, the supports 22 are automatically deployable and the switch30 is not required.

[0046] The electrical cable 32 electronically connects the catheter body14 to the control unit 12. The control unit 12 communicates power,temperature sensor feedback and other signals between the catheter 13and an operator.

[0047] The control unit 12 includes an RF Power supply that couples toan alternating current source and converts typical AC current (e.g., 115VAC/60 Hz US, 220 VAC/50 Hz Europe) into calibrated RF energy.Preferably, the RF energy is within the range of 100 kHz to 3,000 kHz,and more preferably, the RF energy is regulated at about 500 kHz.

[0048] The control unit 12 includes a control panel 38 to enable anoperator to monitor the system 10 and to select a desired heatingprofile to administer. The control unit 12 enables an operator to verifysystem performance. The power supply also provides data acquisitioncapability to record the details of the voltage, current, power,impedance, flow rates and temperatures measured during the procedure.

[0049] According to an aspect of the invention, remotely deployedtemperature sensors detect patient core body temperature and providefeedback to the control unit.

[0050] It is known that the electrical field density between adjacentelectrodes 20 is the highest in the region between the electrodes, andthe field extends radially (with respect to the catheter body 14) outfrom the electrodes 20 with decreasing intensity. The electric fieldwarms the flowing blood. The flowing blood warms the distal end 18 ofthe catheter body 14 and with the electrodes 20.

[0051] The supports 22 position the electrodes 20, and the distal end 18of the catheter body 14 centrally within the blood vessel 34. It can beappreciated that the term “centering” is loosely applied. It ispreferable that the electrodes 20 are centered, not only with respect toa vascular axis, but also accounting for the position where the maximumblood flow rate through the blood vessel 34 is found. Accordingly, wherethe electrodes 20 and the catheter body 14 are coaxially aligned, asshown, “centering” positions the catheter body 18 where the blood flowrate is the highest, apart from the walls of the blood vessel 34.

[0052] It can be appreciated that variations of the invention mayinclude electrodes that deploy in a non-coaxial arrangement with respectto the catheter body. In such embodiments, the electrodes are preferablycentered within the blood vessel 34, while exact centering of thecatheter body is not a necessity.

[0053] Any of a variety of devices can accomplish “centering” inaccordance with the present invention. One way is through the use of thesupports 22. Preferably, the supports 22 are thin and flexible wires.Even more preferably, the supports 22 are flattened to softly engageblood vessel walls. The supports 22 gently flex and a portion of eachsupport 22 radially extends from the catheter body 14 to anchor thecatheter body 14 centrally within the blood vessel 34. The supports 22allow blood to flow through the vessel 34, between the supports 22 andthe catheter body 14.

[0054]FIG. 2(a) and FIG. 2(b) show an aspect of the invention having asensor system with at least one temperature sensor element 42 fixed atthe distal end 18 of the catheter body 14. Preferably, the sensor systemhas multiple temperature sensor elements 42 and one of the sensorelements 42 is positioned adjacent each electrode 20. The electrodes 20define an inside 40, and according to one aspect of the invention, thesensor element 42 attaches to the inside 40 of each electrode 20. Eachsensor element 42 preferably includes a thermocouple, but may include athermistor or other device for detecting temperature in accordanceanother aspect of the invention.

[0055] It can be appreciated that in an alternate embodiment of theinvention, the catheter body 14 includes a resistive, or a fluid basedheating system that cooperates with the electrodes 20. In such anembodiment, the temperature sensors would optimally be positionedelsewhere. An example of a resistive heating system is disclosed in U.S.Pat. No. 6,149,673. An example of a fluid-based heating system isdisclosed in U.S. Pat. No. 6,146,411. The disclosures of these patentsare incorporated herein by reference.

[0056] It can be also appreciated that the sensor system of the presentinvention can be equipped with a pressure transducer attached to thedistal end 18 of the catheter body 14 to facilitate measurement of thelinear and volumetric blood flow rates within the blood vessel 34 (FIG.1).

[0057] The control unit 12 (FIG. 1) monitors the electrodes 20 andsensor system impedances to verify functionality of those components.Should those measured impedances be out of established limits, thecontrol unit provides an alarm.

[0058]FIG. 2(a) shows the supports 22 having two visually definable ends48 and 50 in contact, respectively, with the distal end 18 of thecatheter body 14. The end 48 slideably attaches to the catheter body 14at a first position 44 proximal the electrodes 20. The end 50 slideablyattaches to the catheter body 14 and at a second position 46 distal theelectrodes 20. While the ends 48 and 50 are visually definable, thesupports 22 extend within the catheter body 14 and terminate at theswitch 30 (FIG. 1). The switch 30 selectively retracts the supports 22to cause the supports 22 to lie flush with the exterior of the catheterbody 14 during insertion and removal of the catheter body 14.

[0059]FIG. 3 shows the distal end 18 having two pairs of supports 22extending from the catheter body 14 in a coplanar arrangement. One pairof supports 22 has visually definable ends 52 and 54 that lie flush withthe catheter body 14 in a position proximal to the electrodes 20 whenthe supports 22 deploy. The other pair of supports 22 has visuallydefinable ends 56 and 58 that lie flush with the catheter body 14 in aposition distal to the electrodes 20 when the supports deploy. FIG. 4shows the distal end 18 having two groups of supports 22. One group ofsupports 22 has visually definable ends 52 and 54 that lie flush withthe catheter body 14 in a position proximal to the electrodes 20. Theother group of supports 22 has visually definable ends 56 and 58 thatlie flush with the catheter body 14 in a position distal to theelectrodes 20.

[0060]FIG. 5 shows the distal end 18 having supports 22. Each supportincludes a ring 60 and extensions 62. The extensions 62 mechanicallycouple with the switch 30 and support the ring 60 to selectively deploythe ring 60 against the blood vessel 34 (FIG. 1). The supports 22 form afrustum shape when deployed to facilitate blood flow between the rings60 and the surface of the distal end 18.

[0061] It can be appreciated that the rings 60 and the extensions 62 canbe configured for directing blood towards the electrodes 20. Blood flowsin the direction of the arrow 61.

[0062] According to one aspect of the invention, an insertion tubesurrounds the catheter to hold the supports 22 flush with the distal endof the catheter body. Once the catheter body inserts into the patient,the insertion tube withdraws to allow the supports 22 to automaticallydeploy. Thus the switch 30 is not required.

[0063]FIG. 6 shows the distal end 18 having supports 22. The supports 22each comprise an annular web 64. Blood flows through the web 64. Inaccordance with one aspect of the invention, the web 64 is fabricatedfrom a conductive material that the control unit 12 (FIG. 1) resistivelyheats to warm the blood as the blood flows through the web 64. Each web64 forms a frustum shape in accordance with an alternate embodiment ofthe invention.

[0064]FIG. 7 shows the distal end 18 having supports 22. The supports 22each include pins 66 that extend radially from the distal end 18. Thepins 66 are formed from a pliable material that gently centers thedistal end 18 within a blood vessel. Each pin 66 includes a soft tip 68.It can be appreciated that although the pins 66 deploy radially withrespect to the catheter body 18, that the pins 66 can also deploy at anoblique angle from the catheter body 18.

[0065]FIG. 8 shows the distal end having a single support 22. Thesupport 22 includes multiple pins 66 extending from the surface of thedistal end 18. The pins 66 align in a helix. The support 22 includes ahelical wire 70 that interconnects the pins 66 and provides a helicalsurface for contacting the blood vessel walls. The pins 66 aremechanically coupled with the switch 30 (FIG. 1) to effectuate selectivedeployment of the support 22.

[0066] In Operation:

[0067] During normal operation, the control unit 12 monitors signalgenerated by the sensor system, including the temperature sensorelements 42, any pressure sensor, or any remote temperature sensor. Thecontrol unit 12 automatically increases or decreases the current andvoltage as required to achieve a desired core body temperature. Thecontrol unit 12 continually monitors the impedance of the electrodes(and/or phase angle between the voltage and current) as a measure of thesystem performance and safety. To illustrate, should the impedance showsa sudden rise, this could indicate that an adherent coagulum and/orprotein deposition has manifest on the electrodes. As this condition isdetected, the power level automatically decreases, or ceases, to preventdamage to the blood.

[0068] The system 10 includes a percutaneous introducer set. Theintroducer set preferably includes a short introducing catheter with ahemostat valve, a large bore needle, a short introducing wire, and adilator. In operation, the needle pushes via the skin into the vessel.The introducing wire slides into the vessel, and the needle iswithdrawn. The dilator and introducing catheter track over theintroducing wire, through the muscle, into the vessel 34, or into anancillary vessel such as the femoral artery. Removal of the introducingwire and dilator enables the introducing catheter and hemostat toprovide access to the vasculature. When catheter body 14 inserts intothe vessel 34, the hemostat prevents blood loss.

[0069] The Electric Field:

[0070] The electrodes 20 create an electric field substantially parallelto the catheter body 14. This electric field can be visualized as ahollow cylinder (an annulus) representing a zone of influence thatcircumscribes the distal end 18 of the catheter body 14. This electricfield represents the sum of the electric fields created by theelectrodes 20. The zone of influence affect blood flowing past thecatheter within the bounds of the zone of influence.

[0071] In general, the heating of any incremental volume element ofblood can be expressed as the time integral of the field power that theblood experiences over its path through the zone of influence. The (timeand location varying) instantaneous power can be expressed as the localcurrent squared times the total resistance of that volume element. Notethat the current density will not typically be a constant value, andwill, in general, decrease approximately as the square of the distancefrom the electrode 20. Therefore, the heating of any given volumeelement will be approximately proportional to the fourth power of thedistance of that element from the nearest electrode 20. Note also thatthe temperature rise of any given volume element will be dependentprincipally on the following three factors, the distance from theelectrode 20, the flow rate of the blood, and the total current passingthrough the electrodes.

[0072] The blood temperature at any given moment will be generallyhighest at or immediately adjacent to the electrodes. The bloodtemperature decreases at further distances. Placement of temperaturesensors elements 42 on, or immediately adjacent to, the electrodes 20property permits the monitoring and control of the highest bloodtemperatures by the system 10.

[0073] The present invention is described by way of example only. Thereare many viable embodiments of this invention. For example, the supports22 can be fabricated in any way that allows blood flow between thecatheter 13 and the supports 22 in order to heat the blood. The catheter13 may be warmed by alternate means. The supports 22 can also be warmed.The electrodes 20 can be replaced with any viable radiative heatingelement. Furthermore, the supports 22 may have a variety of shapes andconfigurations other than those disclosed. Accordingly, the invention isto be limited only by the claims as set forth below.

What is claimed is:
 1. A heat exchange catheter for warming blood withina blood vessel comprising: a catheter body having a proximal end and adistal end; electrodes on the distal end of the catheter body forgenerating an electric field that radiates heat to the blood; and ameans for positioning the distal end centrally within the blood vessel.2. A heat exchange catheter as set forth in claim 1, wherein theelectrodes comprise discrete bands that circumscribe the distal end. 3.A heat exchange catheter as set forth in claim 2, wherein each electrodehas a polarity, and for each electrode there is an adjacent electrodehaving an opposite polarity.
 4. A heat exchange catheter as set forth inclaim 3, further comprising a control unit electronically coupled to theelectrodes, the control unit delivering power to the electrodes in thefrequency range of between 100 kHz to 3,000 kHz.
 5. A heat exchangecatheter as set forth in claim 1, wherein the positioning means includessupports having ends and lengths, the ends of the supports attach to thecatheter body, the lengths align longitudinally along the catheter bodyto selectively deploy against the blood vessel to center the catheterbody within the blood vessel.
 6. A heat exchange catheter as set forthin claim 5, wherein the supports include flattened wires.
 7. A heatexchange catheter as set forth in claim 5, wherein the ends of thesupports attach to the catheter body in a position proximal theelectrodes.
 8. A heat exchange catheter as set forth in claim 5, whereinthe ends of the supports attach to the catheter body in a positiondistal the electrodes.
 9. A heat exchange catheter as set forth in claim5, wherein one end of each support attaches to the catheter body in aposition proximal the electrodes, and the other end of each supportattaches to the catheter body distal the electrodes.
 10. A heat exchangecatheter as set forth in claim 5, wherein the distal end of the catheterbody includes a switch mechanically coupled with the supports toselectively deploy the supports.
 11. A heat exchange catheter as setforth in claim 1, wherein the positioning means includes supports havingpins that radially extend from the catheter body to bear gently againstthe blood vessel.
 12. A heat exchange catheter as set forth in claim 1,wherein the positioning means includes supports, each support includes aring and extensions, the extensions support the ring to selectivelydeploy the ring against the blood vessel.
 13. A heat exchange catheteras set forth in claim 1, wherein the positioning means includes a web.14. A heat exchange catheter as set forth in claim 1, wherein a theblood vessel has a wall, the positioning means includes a helical wirefor contacting a blood vessel wall along a helical path, the helicalwire being distanced from the distal end of the catheter body tofacilitate blood flow between the helical wire and the catheter body.15. A heat exchange catheter as set forth in claim 1, wherein thepositioning means includes a web that circumscribes the catheter body,the web being selectively deployable from a first configuration wherethe web lies on the catheter body, to a second configuration where theweb extends from the catheter body to the blood vessel, the web permitsblood to flow through the web when the web holds the catheter bodycentrally within the blood vessel.
 16. A heat exchange catheter as setforth in claim 15, wherein the positioning means achieves a fiustumshape in the second configuration.
 17. A heat exchange catheter as setforth in claim 16, wherein the web warms the blood.
 18. A heat exchangecatheter system for use within a blood vessel comprising: a catheterbody having a proximal end and a distal end; electrodes on the distalend of the catheter body for generating an electric field that radiatesheat to the body cavity, the electrodes being serially aligned on thedistal end and being spaced apart from each other; a control unitelectronically coupled with the electrodes via the catheter body forpowering the electrodes with RF energy; a temperature sensor elementattached to the distal end; and a support for selectively positioningthe electrodes centrally within the body cavity.
 19. A heat exchangecatheter system as set forth in claim 18, wherein the electrodescomprise discrete bands that circumscribe the distal end.
 20. A heatexchange catheter system as set forth in claim 19, wherein eachelectrode has a polarity, and for each electrode there is an adjacentelectrode having an opposite polarity.
 21. A heat exchange cathetersystem as set forth in claim 18, wherein the sensor includes temperaturesensor elements positioned adjacent each electrode.
 22. A heat exchangecatheter system as set forth in claim 21, wherein the electrodes have aninside each temperature sensor element is spot-welded to the inside ofeach electrode.
 23. A heat exchange catheter system as set forth inclaim 22, wherein the electrodes are fabricated from a radiopaque alloy.24. A heat exchange catheter system as set forth in claim 23, whereinthe catheter body defines an exhaust port on the distal end, thecatheter body includes an infusion lumen in communication with theexhaust port for delivering fluids to the distal end of the catheter.25. A heat exchange catheter system as set forth in claim 18, whereinthe control unit delivers power to the electrodes in the frequency rangeof between 100 kHz to 3,000 kHz.
 26. A heat exchange catheter system asset forth in claim 18, wherein the control unit delivers power to theelectrodes in the frequency of about 500 kHz.